1. Field of the Invention
The present invention relates to disk drives and particularly to a flex circuit design for a flex on suspension (FOS) head gimbal assembly (HGA) which achieves reduced pitch and roll stiffness by patterning an insulator substrate of the FOS, and by selectively leaving bare conductive trace sections. The present invention further relates to the protection of magnetoresistive (MR) heads from damage caused by electrostatic discharge (ESD) buildup. More particularly, the invention concerns a method for minimizing cross-talk, noise, and distortion, by depositing a seed layer material on one side of the FOS.
2. Description of Related Art
In a conventional disk drive, a read/write head is secured to a rotary actuator magnet and a voice coil assembly by means of a suspension and an actuator arm, and is positioned over a surface of a data storage disk. In operation, a lift force is generated by the aerodynamic interaction between the head and the disk. The lift force is opposed by a counteracting spring force applied by the suspension, such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the disk.
The suspension includes a load beam and a flexure secured to a cantilevered end of the load beam. A slider is mounted to the flexure. The flexure provides a proper pivotal connection for the slider so that during operation, the slider can compensate for irregularities in the disk drive manufacture and operation, by pitching and/or rolling slightly in order to maintain the air bearing, while maintaining appropriate stiffness against yaw movement. Roll is defined as the rotation about an axis extending directly out from the actuator arm through the pivot connection point and parallel to the X-Y plane of the disk. Pitch is defined as rotation about an axis perpendicular to the roll axis through the pivot contact point and parallel to the X-Y plane of the disk. Yaw is gyration around an axis perpendicular to the air-bearing surface. The flexure has to achieve low enough pitch and roll stiffness for the air bearing flying height tolerances while at the same time achieving high enough yaw stiffness for track seeking. A dimple extends from either the load beam or the flexure tongue, to provide a point load about which the slider gimbals.
As with wires or other types of electrical interconnects, Flex on suspensions (FOS) tend to increase the static pitch and roll angle variations, the gimbal stiffness and the gimbal stiffness variation of the HGA suspension. This results in increased flying height variability of the suspended slider.
Several head designs have been proposed to minimize the stiffness of the FOS circuit, so that the air bearing can more easily overcome the pitch and roll variations of the head. Other head designs have been proposed to reduce pitch and roll changes due to thermal and humidity induced swelling or shrinkage of the polyimide or insulator layer of the FOS.
The following references illustrate various head designs employing flex circuits or insulating layers and conductive traces:
U.S. Pat. No. 4,645,280 to Gordon et al.; PA0 U.S. Pat. No. 4,761,699 to Ainslie et al.; PA0 U.S. Pat. No. 4,819,094 to Oberg; PA0 U.S. Pat. No. 4,996,623 to Erpelding et al.; PA0 U.S. Pat. No. 5,055,969 to Putnam; PA0 U.S. Pat. No. 5,124,864 to Matsuzaki; PA0 U.S. Pat. No. 5,185,683 to Oberg et al.; PA0 U.S. Pat. No. 5,491,597 to Benin et al.; PA0 U.S. Pat. No. 5,528,819 to McKay et al.; PA0 U.S. Pat. No. 5,597,496 to Massaichi et al.; PA0 U.S. Pat. No. 5,598,307 to Bennin; PA0 U.S. Pat. No. 5,606,477 to Erpelding et al.; PA0 U.S. Pat. No. 5,687,479 to Bennin et al.; and PA0 U.S. Pat. No. 5,734,523 to Scheidecker et al. PA0 U.S. Pat. No. 5,055,969 to Putnam; PA0 U.S. Pat. No. 5,644,454 to Arya et al.; PA0 U.S. Pat. No. 5,654,850 to Ganapathi et al.; and PA0 U.S. Pat. No. 5,699,212 to Erpelding et al.
U.S. Pat. No. 5,598,307 to Bennin, supra, is an exemplary reference, and describes laminate structures for use in head suspension assemblies. The laminate structures are intended to eliminate manual handling of conductors by integrating the manufacture of the interconnect assembly with that of the suspension assembly. The first step in the manufacture of the laminate structures is to providing a multi-layer laminate sheet. The sheet comprises a first layer of a metal spring material, an intermediate second layer of an electrically insulating, adhesive material, and a third layer of an electrically conductive material. The second step is to create the layers, starting from the outside in.
The first layer is etched to become the primary spring element. The third layer is etched to provide at least one trace, the trace including at least one elongated conductor configured for electrical coupling to a head assembly and for operation as an additional mechanical spring element in selected regions. The second layer provides panels shaped in conformance with the areas of contact between the structure remaining after the etching to produce the elements of the first and the third layers. The traces of the laminate structure are electrically coupled to a head assembly and the laminate structure is attached to other elements of the head stack assembly. The design includes sections wherein the first and second layers are etched away, leaving the traces of the third layer to serve as both the electrical conductors and the gimbal or flexure.
The Laminate structures include interconnect assemblies, interconnect-suspension assemblies, and gimbal-interconnect assemblies. Interconnect assemblies attach to a load beam and include at least one conductive trace. The second layer provides dielectric insulation and the third layer can include support and stiffening plates. An interconnect-suspension assembly embodiment has a first layer of stainless steel, a thin second layer of polyimide, and a third layer of copper solder mask may be deposited over the copper traces. Gold may be deposited on the copper traces where there is no solder mask.
Many modern disk drives employ MR recording heads that provide improved performance in a number of important respects. However, compared to previous generation thin-film recording heads, MR heads are much more susceptible to damage from ESD. ESD can be generated during the drive operation, or during manufacturing operations.
Several head designs have been proposed to reduce static charge buildup, cross-talk, noise, and distortion. The following patents illustrate some of these head designs:
U.S. Pat. No. 5,055,969 to Putnam, supra, is an exemplary reference, and describes a flexible circuit for an actuator arm of a hard disk storage device. The flexible circuit has a servo preamplifier, a data preamplifier, a signal routing layer which includes a first ground plane, and an electrically conductive second ground plane which is electrically isolated from and closely spaced to the signal routing layer. The flexible circuit includes a flexible substrate which bends so that the actuator arm remains electrically connected to the servo controller and data read/write circuitry when the actuator arm moves the heads from track to track on the disk surfaces. The flexible substrate is multilayered and is formed of a plurality of electrically insulating and conducting layers. The conducting layers include a signal routing layer with a first ground plane which underlies the data and servo preamplifiers and a second electrically floating ground plane layer.
The signal routing layer contains a plurality of data lines which route data between the data head and the data preamplifier and between the data preamplifier and the tail portion. The conductive servo lines are also routed on the signal routing layer. The conductive servo lines route servo data between the servo head and the servo preamplifier and between the servo preamplifier and the tail portion. A conductive, electrically floating second ground plane is incorporated into a layer beneath the signal routing layer. An electrically insulating layer separates the signal routing layer from the second ground plane.
However, there is still a need for a flex circuit design HGA that achieves reduced pitch and roll stiffness, and that further provides ESD protection, and minimizes cross-talk, noise, and distortion.